[QGIS-Developer] set and export FID with OGR provider

[G. Allegri]

HI all,
GeoJSON RFC7946 states that "If a Feature has a commonly used identifier,
that identifier SHOULD be included as a member of the Feature object with
the name "id", and the value of this member is either a JSON string or
number". For example OpenLayers tries to parse the id field to uniquely
identify the features inside a GeoJSON feature collection.
I've digged how OGR GeoJSON driver treats FIDs during serialization and it
seems that it will write it if the OGrFeature has the FID field set [2],
but AFAICS QIGS OGR provider doesn't set it unless "the first attribute is
the FID and the user has set it". Well, this condition depends on [4], and
now I odn't understand how this applies to a QGIS layer being exported to
GeoJSON.

Questions:
 - is there a way to force the OGR provider setting the FID?
 - could the OGR provider have an option to force it from the export
window, like Mapserver does with the USE_FEATUREID option for its output
format

*?*
giovanni

[1] https://tools.ietf.org/html/rfc7946#page-11
[2]
https://github.com/OSGeo/gdal/blob/trunk/gdal/ogr/ogrsf_frmts/geojson/ogrgeojsonwriter.cpp#L601
[3]
https://github.com/qgis/QGIS/blob/master/src/providers/ogr/qgsogrprovider.cpp#L1269
[4]
https://github.com/qgis/QGIS/blob/master/src/providers/ogr/qgsogrprovider.cpp#L894
[5] http://mapserver.org/output/ogr_output.html#table-of-contents
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